The most important relationship you’ll ever have is your relationship with yourself. Feeling whole and satisfied in your being is crucial to a healthy relationship with another. You can’t receive nor give what you don’t offer to yourself. In other words, how you feel and care for yourself sets the foundation for the other relationships in your life. If you don’t love yourself, it’s harder to love others and receive actions of love in return.
When you’re in a romantic relationship, you bring with you all of you (that includes past hurts, traumas, biases, unhealthy patterns, etc ) and therefore unresolved and unhealed parts of you can influence future relationship whether by choosing an unhealthy partner or by potentially sabotaging a relationship
In my opinion, the key is to recognize you’re a complete individual. Meaning that you don’t seek a relationship to complete you. If you are looking to be in a relationship to fulfill a void, you may find yourself disappointed and heartbroken. Learn to be happy and fulfilled as a single individual. Make sure you have goals, interests, all on your own and when dating that this person adds to your life and not simply becomes your life. (Single simply means you are without a romantic relationship. It doesn’t refer to all the other relationships that surround you.)
Be mindful that if you seek a relationship because you’re lonely you will attach yourself to the first person that comes along (whether they have a genuine interests in you or not!). Therefore, have a strong and secure sense of self. Present that self to whom ever you court.